Radiotherapy plus boost to the tumor bed is part of the standard treatment for early stage breast cancer. To deliver the boost by means of intraoperative radiotherapy with electrons (IOERT) is biologically twice as effective as the conventional percutaneous method. A number of prognostic and predictive markers have been described for local control, disease free and overall survival.Recently miRs, which are short non-coding RNAs, were discovered as potential predictors and prognosticators for breast cancer. As opposed to other RNA molecules, miRs are very stable and can therefore be investigated a long time after the tissue sample has been taken. miRNA 375 seems to play an important role in the development and recurrence of breast cancer and should be explored in further studies.